SPECIAL SENSES 12.4 HEARING

SPECIAL SENSES: HEARING Structures of the Ear –Outer Ear Auricle: visible part of the ear –Collects sound waves and directs them towards the external auditory canal

SPECIAL SENSES: HEARING Structures of the Ear –Outer Ear External Auditory Canal: tube which extends from the auricle –Directs sound waves towards the tympanic membrane –Contains Ceruminous glands Produce cerumen (ear wax)

SPECIAL SENSES: HEARING Structures of the Ear –Outer Ear Tympanic Membrane: Ear Drum –Between the external auditory canal and the middle ear –Sound waves cause the eardrum to vibrate

SPECIAL SENSES: HEARING Structures of the Ear –Middle Ear Small, air-filled cavity between the eardrum and the inner ear Eustachian tube (Auditory Tube): equalizes pressure on both sides of the tympanic membrane –connects the middle ear with the upper part of the throat. –Abrupt pressure changes can cause ear drum to rupture

SPECIAL SENSES: HEARING Structures of the Ear –Middle Ear Auditory Ossicles: 3 small bones in the inner ear –Transmit and amplify vibrations from the tympanic membrane to the oval window Malleus: the “hammer” Incus: the “anvil” Stapes: the “stirrup” Oval Window: bony divider between the middle and inner ear – where the inner ear begins

SPECIAL SENSES: HEARING Structures of the Ear –Inner Ear Includes the following: –Cochlea: sense organ for hearing –Vestibule: sense organ for equilibrium –Semicircular canals: sense organ for equilibrium

SPECIAL SENSES: HEARING Structures of the Ear –Inner Ear Cochlea: transmits vibrations to the Organ of Corti Organ of Corti(spiral organ): the organ of hearing –Consist of Supporting Cells Hair Cells: receptors for auditory sensations –Form synapses with sensory and motor neurons of the vestibulocochlear nerve(VIII) –Tectorial Membrane: flexible gel like membrane that covers the hair cells

CHECK FOR UNDERSTANDING 1 1.The organ of hearing 2.Collects sound waves and directs them towards the external auditory canal 3.Equalizes pressure on both sides of the tympanic membrane 4.Receptors for auditory sensations 5.Transmit and amplify vibrations from the tympanic membrane to the oval window 6.Another name for ear wax

SPECIAL SENSES: HEARING Physiology of Hearing –Events involved in the stimulation of hair cells by sound waves 1.Auricle directs sound waves into the external auditory canal 2.Sound waves strike eardrum causing it to vibrate Louder sounds produce larger vibrations

SPECIAL SENSES: HEARING Physiology of Hearing 3.Eardrum connects to malleus causing it to vibrate Vibration moves from the malleus, to the incus to the stapes 4.Stapes moves back and forth pushing the oval window in and out

SPECIAL SENSES: HEARING Physiology of Hearing 5.Oval window bulges inward, pushing on the perilymph fluid Causes fluid pressure 6.Fluid pressure waves are transmitted to the round window

SPECIAL SENSES: HEARING Physiology of Hearing 7.Pressure waves push the vestibular membrane back and fourth Creating pressure waves in the endolymph inside the Cochlear duct

SPECIAL SENSES: HEARING Physiology of Hearing 8.Pressure waves push the in the endolymph cause basilar membrane to vibrate Moves hair cells of the Organ of Corti against the Tectorial Membrane Bending of hair cells causes release of neurotransmitter at sensory neurons Sensory neurons create nerve impulse that travel along the Vestibulocochlear nerve(VII)

SPECIAL SENSES 12.5 EQUILIBRIUM

SPECIAL SENSES: EQUILIBRIUM Physiology of Equilibrium –Two types of Equilibrium 1.Static Equilibrium 2.Dynamic Equilibrium –Receptor organs for Equilibrium are known as the Vestibular Apparatus and consist of the Saccule and Utricle: part of the Vestibule of the inner ear Semicircular Ducts: found inside the Semicircular Canal of the inner ear

SPECIAL SENSES: EQUILIBRIUM Physiology of Equilibrium –Static Equilibrium: maintenance of the position of the body relative to the force of gravity Utricle and Saccule contain Macula Macula: receptor cells for static equilibrium –Hair cells: sensory receptors Hairs protrude into the otolithic membrane If you tilt your head forward gravity pulls the membrane so it slides over the hair cells in the direction of the tilt Stimulates hair cells and triggers a nerve impulse that travels along the vestibulocochlear nerve(VIII)

SPECIAL SENSES: EQUILIBRIUM Physiology of Equilibrium –Dynamic Equilibrium: maintenance of body position in response to sudden movements (rotation, acceleration, etc) Crista: small elevations in the semicircular ducts –Hair Cells: sensory receptors Cupula: gel-like material that covers up the Crista Head moves the hair cells move with it; the endolymph (fluid) lags behind Moving hair cells drag along the stationary endolymph cause hair cells to bend Bending causes electrical signals which cause nerve impulses to travel down the vestibulocochlear nerve(VIII)

CHECK FOR UNDERSTANDING 2 1.Maintenance of the position of the body relative to the force of gravity 2.Together the Saccule, Utricle and Semicircular Ducts are known as the 3.Maintenance of body position in response to sudden movements 4.If using the words Cupula and Crista you are talking about which type of equilibrium 5.Macula and Otolithic membrane describe this equilibrium type 6.Nerve which transmits hearing and balance information